The comments on "Life and Physics" vary wildly, but one recurring theme amongst some commenters is a perception that fundamental physics is too theory-led, that we are obsessed with proving beautiful, reductionist theories and really we should just explore. And that we spend too much time arguing about untestable things.

This is not a criticism to be lightly dismissed, and some of the time, for some physicists, it is almost certainly a fair one. However, I would like to make three counter points.

Thought experiments

In my piece about black holes and fuzzballs, some objected, correctly, that what goes on inside black holes is pretty much inaccessible to experimental test. So why even discuss it? For me, the interest in the discussion is the conflict, in what amounts to an "extreme thought experiment", between three amazingly successful theories, or "laws of physics" if you prefer. Quantum mechanics, gravitation and thermodynamics have their laws, and their underlying picture of the universe. They have credibility by virtue of each being able to describe a vast range of phenomena, ranging from steam engines through planets to the central processing unit in your computer. In a black hole, these laws come into apparent conflict. The territories of three giants overlap. By thinking through the contradictions which arise, we can find gaps in the theories, develop new understanding, and in the end hopefully derive observable predictions which would test such understanding. It is a hugely worthwhile exercise, unless you are utterly uninterested in understanding how things work or in benefiting from such understanding.

Electroweak symmetry breaking

To some it appears the Large Hadron Collider is a disproportionate investment of time, money and expertise in chasing some theorists' dream. I disagree, of course. While the Higgs is the headline, the LHC is genuinely exploring new territory for whatever might be there. The energy frontier (or if you like, the short distance frontier - we study nature at smaller distance scales than anywhere else) remains a frontier of knowledge, whether Peter Higgs says it is or not. Plus, we have very good reason, from experiment alone, to think this part of the frontier is special. Look at this plot:

electron-proton scattering: Credit DESY, ZEUS and H1 experiments.

What is shows is essentially the probability of an electron bouncing off a proton, with the energy of the bounce increasing as you go from left to right. The blue points show the times when it bounces because of its electric charge - the electromagnetic force. The red points are the times when it bounces by swapping a W boson - the weak force. You can see that at low energies (toward the left) the electromagnetic bounce is much more likely. But at high energies (on the right) the weak force is just as likely to be responsible as the electromagnetic. There is a symmetry between the two forces which is restored at this energy*. These are data. Measured. No theory. (The curves are theory, but ignore them.)

The LHC, for the first time in the history of science, allows us to explore properly above that energy, into the region where the symmetry holds. Our theory says the Higgs breaks the symmetry. But even without that theory, you might think exploring physics above this fundamentally important energy scale is an exciting thing to do, and might tell us how these forces work, and why they are sometimes the same and sometimes different.

Gloating

Finally, the LHC data have so far led to a bonfire of theories. While big ideas like supersymmetry or extra dimensions have not been disproved (yet), many many options for them have been closed off.

It is true many of us have our favourite theories, but in the end the data decide, and as an experimentalist I am seriously enjoying making myriad bright ideas face the music. We have waited a long time, theorising and guessing. Now, at last, we are able to look at some more of the answers.

* The scale on the horizontal axis is actually the distance in metres (very small). But where the curves meet is the equivalent of about 100 GeV in energy.